docs: def speed(self, factor, use_semitones=False):
          """speed takes 2 parameters: factor and use-semitones (True or False).
  
          When use-semitones = False, a factor of 2 doubles the speed and raises the pitch an octave. The same result is achieved with factor = 1200 and use semitones = True.
          """
          self.command.append("speed")
          self.command.append(factor if not use_semitones else str(factor) + "c")
          return self